Customs: I need some advice/help "about building fort max head"

I'm making a classic's Fort Max out of a spare unicron body I had laying around. While I got just about everything planned out so far I am still having trouble with the head.

I really have no idea on how I should handle it, at first I was going to just use a superion head like other have. But I quickly discovered that the head is WAY to small for unicrons body.

Then I noticed that Energon Omega Supreme's head would be absolutely perfect and it is even a headmaster! But, your more likely to find a leprechaun riding a unicorn than you are a Energon Omega Supreme head by itself.

So now I am at a loss, I really want it to be a headmaster like the original. But I really have no means to succeed because most solutions are either to small or to large to work, or it is just plain impossible to get the part.

Perhaps I could sculpt a head then use styrene for simple joints. But I really have no idea how I would do this, since all I really have to scuplt is some "epoxy putty" that walmart sells in automotive. I also cant use sculptit since I don't have easy access to a kelm.

Does anyone have any ideas? Like I said, it has to look nice on unicrons body, and be able to have a bionicle ball joint put in it "although thats not much of a problem "